1. Field of the Invention
The present invention relates to a method of manufacturing a photoelectric conversion device and relates, more particularly, to a method of manufacturing a photoelectric conversion device with Cu for wiring.
2. Description of the Related Art
Photoelectric conversion devices are frequently used as a sensor for digital cameras. In the recent years, as such a photoelectric conversion device, an MOS photoelectric conversion device with a plurality of MOS transistors pixel readout circuit is used.
MOS photoelectric conversion devices respectively require wiring for driving MOS transistors and wiring for reading signals. Therefore, wiring increases in number in comparison with a CCD. Accordingly, multilayered wiring structure with a plurality of wiring layers being stacked through interlayer insulation film is adopted. For such wiring material, conventionally aluminum has been used frequently. In contrast, use of Cu as wiring material in order to decrease size of wiring pitch further and otherwise in order to make film thickness of wiring thinner to decrease height of a photoelectric conversion device is described in Japanese Patent Application Laid-Open No. 2003-264281.
In addition, in a photoelectric conversion device, defects in a semiconductor substrate occasionally served as a source of generating a dark current to cause deterioration in signals. In contrast, techniques of supplying the semiconductor substrate with hydrogen to terminate dangling bond of a substrate surface (hydrogen terminating techniques) are proposed. As one of the hydrogen terminating techniques, Japanese Patent Application Laid-Open No. 2003-264277 has disclosed forming a contact plug made of tungsten and thereafter heating in one of an atmosphere including nitrogen and hydrogen and a hydrogen atmosphere.
It is important to cause a photoelectric conversion device to undergo hydrogen termination in order to recover the crystal defect and the interface state of a semiconductor substrate. However, for supplying a semiconductor substrate with hydrogen, temperature thereof is important. Therefore, conducting thermal processing with one of a constant and higher temperature is required.
However, thermal processing after forming wiring occasionally may lead to increase in wiring resistance and stress migration of wiring material in the case of a high temperature of, for example, 400° C. or more. In particular, in the case of adopting Cu for wiring material, the above described increase in wiring resistance and stress migration of wiring material occasionally take place at a temperature lower than in the case of aluminum. Moreover, depending on temperature for thermal processing and time for processing, diffusion of Cu to the front side from the rear side of a semiconductor substrate occasionally gives rise to a problem. Attachment of a certain amount of Cu on the rear side of the semiconductor substrate during a film forming step is considered to be a reason thereof.
That is, in the case of using Cu as wiring material, hydrogen terminating processing in the case where the wiring material is aluminum, that has been frequently used to date, cannot be directly used. Terminating processing suitable for the case of using Cu as wiring material has not been considered sufficiently.
Moreover, in Japanese Patent Application Laid-Open No. 2003-264277, thermal processing is conducted by depositing tungsten in a contact aperture and thereafter removing tungsten outside the contact aperture. However, hydrogen for recovering the crystal defect and the interface state of a semiconductor substrate is not sufficiently supplied and consequently a sufficient dark current reducing effect is occasionally not obtainable. That is, conducting thermal processing alone in a hydrogen atmosphere will cause hydrogen to leave toward the upper part of a semiconductor substrate at the same time when hydrogen is supplied.
In view of the above described problem, an object of the present invention is to provide a method of manufacturing a photoelectric conversion device enabling suitable hydrogen terminating processing even in the case of using Cu for wiring material.